As one of the sensors used for biomolecular analysis or the like, a sensor that makes use of the phenomenon in which the light intensity of the reflected light having a particular wavelength is attenuated by surface plasmon resonance is proposed, and a surface plasmon sensor basically constituted by a prism-shaped dielectric block, and a metal film formed on the block, and brought into contact with the specimen is disclosed, for example, in Japanese Unexamined Patent Publication No. 6 (1994)-167443. In the sensor, total reflection occurs at the interface between the dielectric block and the metal film. When testing a specimen, measuring light is irradiated on the sensor such that total reflection attenuation occurs by the surface plasmon resonance, and the intensity of the reflected light totally reflected at the interface is measured to detect the total reflection attenuation. In this way, measurement of the refractive index or density of the specimen, identification of the specimen, or the like is performed.
The plasmon sensor described above is expensive, since it requires the prism-shaped dielectric block. Further, it has many structural constraints, so that down-sizing of the sensor or simultaneous analysis of multiple specimens is difficult. Consequently, a different type of sensor that makes use of the phenomenon in which the light intensity of the reflected light having a particular wavelength is attenuated by local plasmon resonances is proposed, and a local plasmon sensor having microscopic metal relief structures on the surface of the substrate for effectively inducing local plasmon resonances is disclosed as described, for example, in Japanese Unexamined Patent Publication No. 2004-232027, or nonpatent literature, “Local plasmon sensor with gold colloid monolayers deposited upon glass substrates” by Takayuki Okamoto and Ichirou Yamaguchi, OPTICS LETTERS, Vol. 25, No. 6, pp 372-374, Mar. 15, 2000.
The local plasmon sensor described above has a simpler structure, and is less expensive with less structural constraints compared with the surface plasmon sensor, since no prism-shaped dielectric block is required. The local plasmon sensor, however, has less favorable detection sensitivity than the surface plasmon sensor so that accurate analysis is difficult.